In the past it has not been economically feasible to situate certain sophisticated communication systems in sparsely populated areas because of insufficient demand for service. For example, automated operator service has generally been provided only in highly populated areas. However, very recently it has become feasible to provide such service to rural communities through the provision of relatively small remote communication systems which are controlled by a single central communication system including a large data processing unit.
Although these small communication systems are remotely situated in relation to the central unit, they must still provide high quality reliable service. Reliability is essential so that customers served by these systems will not experience any inconvenience even when equipment troubles develop in the communication paths between the remote systems and the central system, or in the remote systems themselves. To meet this high standard, major functional equipment will often be duplicated. For example, each remote system may itself be duplicated with duplicated data paths to the central system. Each data path may even have sufficient information handling capacity to fully handle the normal data load between the remote system and the central system.
In one prior art system, each duplicated system half of a remote system independently generated reports and independently communicated such reports to the central system over a dedicated data path. The central system would compare the reports from each half with a mismatch indicating a potential malfunction at the remote location. It is apparent that the malfunctioning remote system half must be identified as quickly as possible to maintain system integrity. If maintenance personnel are stationed at the remote system, they can institute manual diagnostic routines to identify any malfunctions. However, normally, it is not economically feasible to provide highly skilled maintenance personnel at each remote location. Accordingly, the trend today is toward centralized maintenance, and in this prior art system the central system itself was adopted to perform all diagnostic routines on the remote system. This was accomplished by sending diagnostic commands over the data paths and waiting to receive reports from each remote system half. These reports were then evaluated to identify any malfunctions.
Once a malfunction was detected, the suspect remote system half and associated data path were taken out-of-service, and all normal communication services were provided by the in-service half utilizing the in-service data paths for the conveyance of all information. To pinpoint the actual cause of the problem in the suspect half, a very large number of additional diagnostic commands were conveyed by the central system to the suspect half over the inservice data path, and a corresponding number of replies were conveyed back to the central system over this inservice data path. This large number of additional reports and commands tended to clog the in-service path and inhibited the conveyance of normal information thereover.
It is an object of this invention to perform effective and thorough diagnostic operations on remotely situated duplicated communication units, minimizing the use of the in-service data path connecting these remote units to a controlling data processor, so that this data path can be utilized primarily for the conveyance of actual processing information.